1. Field of the Invention
The present invention relates to a process for extracting poly-beta-hydroxybutyrates from an aqueous suspension of microorganisms, in which an azeotropic distillation, coupled to an extraction by solvent, is carried out.
2. Background of the Art
Many microorganisms are capable of synthesising poly-beta-hydroxybutyrates, the main function of which in these microorganisms appears to be the storage of energy in the form of carbon-containing material. These poly-beta-hydroxybutyrates (PHB) constitute a raw material which is of value from the industrial standpoint. Many techniques have already been envisaged to separate them from the biomass.
Thus, it was already proposed in Patent Application EP-A No. 0,015,123 to dry the bacterial cells by introducing a hot gas in a first stage, and then, after cooling in a second stage, to extract the poly-beta-hydroxybutyrates with a suitable solvent. To this two-stage process, supplementary stages may be added such as, in particular, a stage in which the bacterial cells are lysed before extraction with the solvent.
Another process is described in Patent Application EP-A No. 0,046,017. According to this document, the bacterial cells are flocculated at a high temperature by modifying the pH in a first stage, and then, in a second stage, after cooling, the suspension of flocculated bacterial cells is heated by introducing water vapour under pressure; this operation is followed or preceded by an additional modification of the pH. The flocculated cells are then dried so as to obtain a porous granular product, for the purpose of subsequent contact with the solvent for extraction of the PHB.
In Patent Application EP-A No. 0,058,480, another process requiring several stages has been described. According to this process, the bacterial culture is first dried by spraying at a high temperature, and the dried cells, after being cooled, are then brought into contact with methanol for the purpose of extracting the lipids, and finally with a solvent for the purpose of extracting the poly-beta-hydroxybutyrates. The solution is then further cooled below 0.degree. C., and then heated to 20.degree. C. for 30 minutes, a gel thereby being obtained. This gel is subjected to pressure for the purpose of expelling the solvent.
The processes of the prior art nevertheless have disadvantages when they are carried out in industrial installations, on account of the complexity imposed on the installations and the high energy expenditure resulting from the successive heating and cooling.